The present invention relates to a presensitized plate for use in making a lithographic printing plate which makes it possible to form printed matters without using no dampening water.
There have been proposed a variety of presensitized plate for use in making a lithographic printing plate requiring no dampening water (the presensitized plate is hereinafter referred to as "water-less PS plate" and the resulting lithographic printing plate is referred to as "water-less lithographic printing plate). Among these, those which comprises a substrate provided thereon with in order a photopolymerizable light-sensitive layer and a silicone rubber layer have very excellent quality and examples thereof are, for instance, disclosed in Japanese Patent Publication for Opposition Purpose (hereunder referred to as "J.P. KOKOKU") Nos. Sho 54-26923 (U.S. Pat. No. 3,894,873) and Sho 56-23150. These photopolymerizable light-sensitive layers undergo a polymerization reaction through a radical polymerization which is inhibited by oxygen. For this reason, Japanese Patent Unexamined Publication (hereunder referred to as "J.P. KOKAI") No. Sho 50 59101 proposes the use of an oxygen-impermeable coating layer of a substance such as polyethylene terephthalate, cellophane, polyvinylidene chloride, polyvinyl chloride, polyvinyl alcohol, polypropylene or polyethylene. If a cover coat obtained from a low oxygen-permeable polyethylene terephthalate or polyvinylidene chloride is employed, the polymerization is not inhibited by oxygen, but the polymerization reaction is initiated in half-exposed and/or non exposed portions of the light-sensitive layer as soon as the PS plate which is not exposed or imagewise exposed to light is kept to stand under irradiation of white light rays, hence so-called "fogging" phenomenon arises and it is correspondingly impossible to develop the plate. If polyethylene or polypropylene which has relatively high oxygen permeability is used, the problem of "fogging" does not arise even if it is kept to stand under the irradiation of white light rays, but when it is imagewise exposed to light with a vacuum contact printer, the degree of polymerization-inhibition varies depending on the degree of vacuum of the printer and correspondingly the sensitivity and tone reproduction are different between the central portion and the edge portion of the plate.